Halogens and alkali metal hydroxides have been conventionally produced by the electrolysis of aqueous alkali metal halide solutions in diaphragm-type cells. Such cells generally have an opposed anode and cathode separated by a fluid permeable diaphragm, usually of asbestos, forming separate anode and cathode compartments. In operation, brine is fed to the anode compartment wherein halogen gas is generated at the anode, and the brine then percolates through the diaphragm into the cathode compartment wherein alkali metal hydroxide is produced. The alkali metal hydroxide thus produced contains large amounts of alkali metal halide, which must be removed by further processing to obtain the desired product.
Recently, electrolytic cells have been developed which utilize a permselective cation-exchange membrane in place of the conventional diaphragm. Such membranes, while electrolytically conductive under cell conditions, are substantially impervious to the hydrodynamic flow of liquids and gases. In the operation of membrane cells, brine is introduced into the anode compartment wherein halogen gas is formed at the anode. Alkali metal ions are then selectively transported through the membrane into the cathode compartment. The alkali metal ions combine with hydroxide ions generated at the cathode by the electrolysis of water to form the alkali metal hydroxide.
Membrane-type electrolytic cells have numerous advantages over conventional diaphragm cells, including the production of relatively pure alkali metal hydroxide in high concentrations, the production of more halogen per unit of cell volume, and the ability to operate at higher, more efficient, current densities. However, ion permeable membranes used in such cells are not readily adaptable to the angular and planar configuration of conventional cell apparatus. Additionally, due to their relatively soft and flexible nature, it is often difficult to position the membrane relative to the electrodes and to obtain a reliable seal at the membrane-cell wall joints.
Accordingly, it would be highly desirable to provide a cell design which retains the advantages inherent in use of the membranes, while avoiding the disadvantages.